1. Field of the Invention
This invention relates to multi-speed transmissions and, more particularly, to a multi-speed transmissions having a main and range gear reduction section.
2. Description of the Prior Art
It is elementary that meshing gears rotate in opposite directions; that is, one will rotate in a clockwise direction and the other in a counter-clockwise direction. In a multi-speed transmission, the main shaft will have a number of ratio gears which are driven by meshing countershaft gears, and speed selection is made by clutching one of the main shaft ratio gears to the main shaft. If reverse direction is to be selected, the main shaft gear for reverse direction must be rotating in a reverse direction compared to the forward ratio gears. This requires the use of an idler gear between the driven countershaft gear and the main shaft gear. This in turn requires a separate shaft for mounting the reverse idler gear.
A separate shaft is used for mounting the reverse idler gear in both a single box transmission and a transmission having a main and range section wherein the main section provides a plurality of gear ratios, and the range section selectively multiples a gear ratio provided by the main section.
Separate shafts are also used for mounting the reverse idler gears in a single box transmission and a transmission having a main section and a range section wherein multiple countershafts are used. A separate shaft would be required for each countershaft of the multiple countershaft transmission.
In multi-speed automotive transmissions carrying heavy torque loads, the single countershaft transmission becomes quite large, and a multi-countershaft transmission becomes attractive to reduce size, carry heavier torque loads, increase gear life, and reduce costs.
In multiple countershaft transmission much effort has been expended on developing ways to insure even distribution of the torque load among the countershafts. This effort has been largely centered in attempts to allow the main shaft to float within limits so that it can seek its own center and distribute the torque load among the countershafts. In my co-pending patent application entitled "Twin Countershaft Transmission With Floating Main Shaft", filed concurrently herewith, on Sept. 25, 1987 as Ser. No. 101,065, and still pending a transmission with a fully floating main shaft is set forth.
While the multi-countershaft transmission has reduced the overall transmission size and complexity for a given torque rating and the twin countershaft transmission set forth in my aforementioned patent application has optimized such advantages, the inherent requirement of having separate shafts for the reverse idler gears has not heretofore been overcome.